Cryogenic insulations are needed to minimize heat transfer into storage tanks and transfer lines for cryogenic liquids. There are several types of insulation classified based on cost, weight, ease of application, and thermal conductivity. Expanded foams, gas-filled powders, and fiber materials provide insulation through a cellular or porous structure that reduces conduction and convection. Vacuum, evacuated, and opacified powder insulations further reduce conduction and radiation by removing gases. Multilayer insulation uses alternating conductive and non-conductive layers under vacuum to maximize reflection of radiation for optimal heat transfer prevention. The type used depends on the insulation needs and limitations of the specific cryogenic system.

1. Cryogenic Insulations
By-
Dhiraj Powar
PRIYADARSHINI INSTITUTE ENGINEERING AND TECHNOLOGY
NAGPUR
DEPARTMENT OF BIOTECHNOLOGY

2. 1.Introduction
2.Need
3.Classification
4.Advantages
5.Disadvantages
Insulation
Contents

3. Introduction
• In today’s world, the use of cryogenics and low-temperature
refrigeration is taking a more and more significant role.
• From the food industry, transportation, energy, and medical
applications to the Space Shuttle, cryogenic liquids must be
stored, handled, and transferred from one point to another.
• To minimize heat leaks into storage tanks and transfer lines,
high-performance materials are needed to provide high levels
of thermal insulation.
• For progress and efficiency into the 21st century, high
performance thermal insulation systems are needed….

4. Different modes of heat transfer are:
1. Conduction: The heat is
conducted through lateral beams,
neck and residual gas conduction.
2. Convection: The air between
inner and outer vessels convert
heat into the liquid.
3. Radiation: The radiation heat
transfer from 300 K outer vessel
to 77 K inner vessel.
What is need of Insulations ?

5. • Expanded foams
• Gas filled powders& fibrous
materials
• Vacuum
• Evacuated powders & fibrous
materials
• Opacified powders
• Multilayer insulations
Types of
Insulation
• These insulations listed in order of the increasing Cost and Performance .
• Several types of insulation are used in Cryogenic applications .
Classification

6. Continue…
1.Cost
3.Ease of Application
2.Weight
4.Ruggedness
5.Effectiveness
6.Thermal Conductivity
• For a Particular system ,the specific insulations to be used is
determined by-

7. 1.Expanded Foam Insulation
• Structure & Construction:

8. • It’s Cellular structure is formed when evolving gas during
foam formation .
• Some Examples- Polyurethane foam ,Polystyrene foam,
Rubber, Silica & Glass foam.
• The thermal conductivity of this insulations depends on the
Foaming gas, Internal radiant heat transfer and Solid
conduction .
• The foaming gas is CO₂, which is widely used because it has
low Vapor pressure at Liquid Nitrogen temperature .

9. • The thermal conductivity of the fresh foam is initially decreased when
one side is cooled to Liquid N₂ temperature because much of the CO₂
condenses within insulation .
• After the foam has been exposed to ambient air for a few months, then
the thermal conductivity may increases as much as 40 % because of air
diffuses into the cells and replaces some of the CO₂.
• When the foam exposed to atmosphere containing H₂, He gas , the
thermal conductivity may be increased up to 3-4 factor .
• If the foam were fitted closely around a LN vessel , the foam would
crack during cool-down because it shrinks more than the metal inner
vessel .

10. Sr.No Foam Density Thermal Conductivity
Kg/m³ Lbm/ft³ mW/m-K Btu/hr-ft-ᵒF
1. Polyurethane 11 0.70 33 0.019
2. Polystyrene 39
46
2.4
2.9
33
26
0.019
0.015
3. Rubber 80 5.0 36 0.021
4. Silica 160 10.0 55 0.032
5. Glass 140 8.7 35 0.020
Thermal Conductivity of some foam insulations :
• Table 1: Apparent thermal conductivity of foam insulations for
boundary temperature of 330 k and 77K

11. Foam Insulation
Advantages
• Low cost
• No need of rigid vacuum
jacket
• Good mechanical Strength
Disadvantages
• High thermal contraction .
• Conductivity may change
with time.
• The foams can be used as insulation if contraction joints are
provided in foam and if foam is enclosed with plastic liner such
as Myler to prevent diffusion of water vapor & air into the
joints .

12. 2.Gas-filled powders & Fibrous materials
• This includes fiber glass ,powdered cork ,Perlite ,Santocel,
rock wool & Vermiculite.
• The small sizes of voids within the material are responsible
for the reduction/ elimination of convection .
• In case of fine powders , the mean free path of gaseous
conduction shifts from continuum to free – molecular gaseous
conduction

13. Sr.No Insulations Density Thermal Conductivity
Kg/m³ Lbm/ft³ mW/m-K Btu/hr-ft-ᵒF
1. Perlite 50
210
3.1
13.1
26
44
0.015
0.025
2. Silica aerogel 80 5.0 19 0.011
3. Vermiculite 120 7.5 52 0.030
4. Fiber glass 110 6.9 25 0.014
5. Rock wool 160 10.0 35 0.020
Thermal Conductivity of gas-filled powders & fibrous
material insulation :
• Table 2: Apparent thermal conductivity of gas-filled powders &
fibrous material insulations for boundary temperature of 330 k
and 90K.

14. Gas filled powder& Fibrous material Insulation
Advantages
• Low cost
• Easily applied to irregular
shapes
• Not flammable
Disadvantages
• Vapor barrier required .
• Conductivity may increase
when powder packed
• Hydrophilic nature

15. 3.Vacuum Insulation
• This insulations extensively
used for small laboratory-size
Dewar's.
• It eliminates two components of
heat transfer–
1.conduction
2.convection
• Heat transfer due to – radiation
• Heat transfers from hot outer
jacket to the cold inner vessel &
by gaseous conduction through
the residual gas within annular
space Vacuum insulated cryogenic pipe system

16. Vacuum Insulation
Advantages
• Easily applied to
Complicated shapes
• Small –cool down loss
• Low heat flux for small
thickness
Disadvantages
• A permanent high Vacuum
is required .
• Low-emissivity boundary
surfaces needed

17. 4.Evacuated powder & Fibrous material
• To reduce the heat transfer rate through these insulation ,evacuate
the gas from the insulation.

18. Figure: Variation of mean apparent thermal conductivity with residual gas
pressure for an evacuated-powder insulation .

19. • For highly evacuated powders & fibrous insulations near
room temp ,the radiant contribution is larger than the solid
conduction contribution to the total heat-transfer rate .
• On the other hand, the radiant contribution becomes small
for temp between LN & LH or Helium .
• For this reason ,evacuated powders are superior in
performance compared with vacuum alone.
• We can use –Perlite ,Silica aerogel, Calcium-silicate,
Lamblack,Fiberglass as a in insulation material which has
less thermal conductivity at boundary conditions.

20. 4.Evacuated powder & Fibrous material
Advantages
• Vacuum level less stringent
• Complicated shapes may
easily insulated
• Relatively easy to evacuate
Disadvantages
• May pack under vibratory
loads or thermal cycling
• Vacuum filters are required
• It retains moisture ,so it
must be protected .

21. 5. Opacified-powder insulation
• The performance evacuated powders could be improved by
reducing radiant heat transfer .
• This improvement is accomplished by addition of Copper or
Aluminum flaks to evacuated powders.
• By using optimum amount of opacifer ,the thermal
conductivity of an evacuated powder can be reduced .
• According to safety point of view, copper flaks is preferable
than aluminum becoz aluminum has large heat of combustion
with oxygen

22. Opacified- Powder insulation
Advantages
• Better performance than
evacuated powders
• Complicated shapes may
easily insulated .
• Vacuum require is not
stringent
Disadvantages
• High cost
• Explosion hazardous with
Aluminum in ox an oxygen
atmosphere
• Settling of Metallic flakes
Examples:- Copper-santocel
Aluminum-santocel
bronze-santocel
Silica- carbon

23. 6.Multilayor insulation
• The multilayer insulations consist of
alternating layers of highly reflecting
materials like- aluminum foil, copper foil,
aluminized Mylar,& low conductivity
spacer such as fiberglass or paper mat
,glass fabric ,nylon mesh .
• The layers may also be separated by
crinkling or embossing the sheets so that
they touch only at discreet point & a
spacer is not required .

24. • The multilayer insulations must be evacuated to pressure below
10 mPa.
• It has low thermal conductivity .
• Radiation is minimized by using many layers of metal foil while
solid conduction through spacer is removed by using a low
conductivity fibrous material and gaseous conduction is
minimized by reducing residual gas pressure .
• The bulk density of insulation material is depends on the
thickness and density of reflective shields.

25. Multilayer insulations
Advantages
• Best performance
• Low weight
• Lower-cool down loss
• Better stability
Disadvantages
• High cost
• Difficult to apply on
complicated shapes
• Problems with lateral
conduction
• More stringent vacuum
requirement